<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>在线尝试 Bootstrap 实例</title>
    <meta name="viewport" content="width=device-width,
                                     initial-scale=1.0,
                                     maximum-scale=1.0,
                                     user-scalable=no">

    <link rel="stylesheet" href="css/bootstrap.css">
    <script src="js/jquery-3.2.1.js"></script>
    <script src="js/bootstrap.js"></script>
</head>
<body>
<div class="container">

    <div class="dropdown">
        <button type="button" class="btn dropdown-toggle" id="dropdownMenu1"
                data-toggle="dropdown">
            主题
            <span class="caret"></span>
        </button>

        <ul class="dropdown-menu" role="menu" aria-labelledby="dropdownMenu1">
            <li role="presentation">
                <a role="menuitem" tabindex="-1" href="#">Java</a>
            </li>
            <li role="presentation">
                <a role="menuitem" tabindex="-1" href="#">数据挖掘</a>
            </li>
            <li role="presentation">
                <a role="menuitem" tabindex="-1" href="#">数据通信/网络</a>
            </li>
            <li role="presentation" class="divider"></li>
            <li role="presentation">
                <a role="menuitem" tabindex="-1" href="#">分离的链接</a>
            </li>
        </ul>
    </div>






</div>
</body>
</html>